Wireless electronic locking and unlocking systems are known from the automobile industry. For example, magnetic antennae are installed in automobile door handles, in door frames, side panels or bumpers of motor vehicles, to transmit or receive an electromagnetic signal in order to allow a wireless communication, e.g. for communicating with a transceiver of a key. To accommodate a transmit-receive antenna in a bent door handle the magnetic core is designed, for example, as a rod core of a longitudinal shape, which is formed of several tape-shaped layers of a soft-magnetic metal alloy, wherein the bending tolerance of the layer stack goes from limited to small. Therefore, the core of these antennae may be subjected to stress, resulting in altered magnetic properties if the deformation is too strong, as great tensile forces and compressive forces occur in the material in the layer levels. Moreover, the basis materials of these so-called tape cores are significantly more expensive than those for ferrite cores, and the magnetic losses of more inexpensive, iron-based amorphous cores, as compared to ferrites, are clearly greater at frequencies above 100 kHz. Conventional methods for the production of those antennae using tape cores additionally have the drawback that the stacking of the tapes is relatively complicated.
Antennae with cores made of ferrite rods that have a bent or very long shape are difficult to realize, or not at all, due to the production method. Examples for a bent ferrite core rod are described in DE 101 28 406 B4 and DE 10 2007 007 117 A1. The production of a ferrite core requires the mixing of a presintered magnetic powder with a special plastic injection granulate, which is injected to obtain the desired shape.
In the production of bent or long antennae mechanical strains in the ferrite core rod itself, or external impacts, may result in the breakage of the core, and thus in a deterioration of the magnetic properties. Also, the fabrication of particularly long rod cores having comparatively small core cross-sections is subject to restrictive technical rules, according to which the length of rod cores has to be in a special proportion to the cross-section, respectively, cross-sectional shape. The reasons for this reside in the necessary uniform compression of the magnetic powder, the technically possible stroke of the pressing devices, the mechanical stability during the transport to the sintering devices, the possible strain during the sintering, and the mechanical stability of the finished magnetic ceramics. Thus, it is difficult to produce long rod cores with lengths, for example, of up to 30 cm or more, which would be necessary for a significantly greater coverage of LF antennae with a frequency, for example, of approximately 125 kHz.
For forming a bent or long ferrite core rod it is also possible to connect several core elements having straight or beveled plane end sections to a bent or straight shape. However, configurations of this type have the disadvantage that the adhesive joints of the rod cores glued together could become undone, on the one hand. On the other hand, in the case of a very good bonding strength, the cores can break undefinably even under a small bending load. The air gaps thus created change, respectively, deteriorate the efficiency of the antennae, as compared to an antenna core formed of one piece. Also, ferrite rod core antennae of this type are relatively unstable in terms of magnetism and temperature, and are subjected to great fluctuations in the magnetic stray fields on account of the changing air gaps.